This invention relates to a seal means for electrolysis cells and a method of sealing electrolysis cells.
Electrolysis cells are used in various applications, for example, electrolyzing an alkali metal salt, such as sodium chloride, to produce a halide and alkali metal hydroxide, such as chlorine and sodium hydroxide. A typical structure for an electrolysis cell is that of the filter press-type, which includes monopolar or bipolar structures. Bipolar structures, for example, are as described in U.S. Pat. Nos. 4,108,742 and 4,111,779.
Typically, a seal means for an electrolysis cell, in particular a filter press-type cell, well known in the art, includes a gasket placed between two adjacent electrode frame members forming an electrolysis cell assembly. A compressive force is applied to the entire cell assembly to squeeze the elements together to form a fluid-tight, i.e., liquid- and gas-tight, seal. The compressive force typically is applied manually or may be applied utilizing hydraulic rams or other types of pressure-applying apparatus to compress the electrode frame members and gasket together. Upon compression, it is common for conventional gasket material, such as rubber or elastomer to deform and expand outwardly or "ooze-out" of the electrolysis cell assembly as pressure is applied to the frames via the frame members. Gaps between cell frame members, caused by gasket oozing out, may lead to gas or electrolyte leakage especially in pressurized cells, requiring shutdown of the cell's operation. Furthermore, in cells employing a separator or membrane, as the gaskets deform outwardly, certain separators which are in contact with the gaskets tend to stretch when they are pulled under the pressure of the outwardly deforming gaskets. The stretching of the separator by gasket deformation can cause the separator, which typically is a flat, thin, sheet-like membrane, to break or tear during compression of the gasket and frame members.
Any tears or breaks in the membrane employed in a cell may lead to reduced current efficiency during operation of the cell, greatly increasing electrical current usage while reducing the electrolytic operating efficiency of the cell. Too great a drop in current efficiency and/or electrolytic operating efficiency can require costly shutdown of the entire cell while the damaged membrane or membranes are replaced.
In order to achieve a fluid-tight cell, conventional seal means require a large amount of compressive force for adequate interface tightness between the cell frame members and membrane to prevent electrolyte leakage. This compressive force may become so large as to cause stretching of or damage to the thin and relatively weak membrane. Thus, mechanical failures of the membrane have been attributed to the mechanical inadequacies of the interface seal assemblies employed hitherto, and the service life expectancy of flat, sheet-like membranes for electrolysis cells have been known to be significantly effected by gasket characteristics and by the mechanics of sealing. It is desirous to elongate the service life of the membrane by providing a seal means which minimizes stretching of or damage to the membrane and thus, minimize production stoppages. Furthermore, elimination of gas and electrolyte leakage is desirous as such leakages may cause a safety hazard.